1. Field of the Invention
The present invention relates to an angular velocity measuring device preferably used for detecting an angular velocity, for example.
2. Description of the Related Art
Generally, an angular velocity measuring device in which an angular velocity detection element and a signal processing element are mounted is known (see Japanese Unexamined Patent Application Publication No. 10-300475, for example). In this case, the angular velocity detection element is defined by a vibrating body arranged so as to be vibrated in first and second axial directions out of three axes at right angles to each other, a driving element for making the vibrating body vibrate in the first axial direction by a drive signal, and a displacement detecting element for detecting a displacement in the second axial direction of the vibrating body and outputting a detection signal when an angular velocity is applied around the third axis while the vibrating body is vibrated in the first axial direction. Furthermore, a drive wiring and a detection wiring connected to the driving element and the displacement detecting element of the angular velocity detection element, respectively, are contained in the substrate, and the angular velocity detection element and the signal processing element are connected through the wiring.
In the angular velocity measuring device according to such a related technology, when a drive signal is inputted from the signal processing element to the angular velocity detection element through a drive wiring, the driving element makes the vibrating body vibrate in the first axial direction on the basis of the drive signal. In this state, when an angular velocity is applied around the third axis, a Coriolis force operates on the vibrating body in the second axial direction. In this way, since the vibrating body is displaced in the second axial direction in accordance with the angular velocity, the displacement detecting element detects the amount of displacement of the vibrating body in the second axial direction as a change of electrostatic capacitance, etc., and outputs a detection signal in accordance with the angular velocity. Then, the signal processing element receives the detection signal from the displacement detecting element through the detection wiring and calculates the angular velocity by performing various calculation processes concerning the detection signal.
Since the detection wiring has a high impedance on the order of megaohms (×106Ω), in the above-described related technology, crosstalk occurs due to a coupling capacitance between the drive wiring and the detection wiring and there are cases in which drive signals mix into a detection signal. At this time, since both the drive wiring and the detection wiring according to the related technology are disposed on the surface of the substrate, sufficient shielding cannot be provided around the detection wiring having a high impedance and the coupling capacitance between the drive wiring and the detection wiring cannot be reduced. Accordingly, in the related technology, the drive wirings and the detection wirings transmit two drive signals and detection signals having different signs, and the balance of coupling capacitance between the drive wirings and the detection wirings is adjusted to cancel crosstalk.
However, in such a construction according to the related technology, since the coupling capacitance between the drive wiring and the detection wiring has a large absolute value, a small amount of coupling capacitance (a few fF, for example) remains because of variations of the wirings, etc. At this time, when a weak angular velocity is detected, for example, since the detection signal is also very weak, even if the crosstalk is caused by a very tiny coupling capacitance a very large output at rest is generated in comparison with the detection sensitivity. As a result, there is a problem in that the deviation of output at rest and offset temperature drift characteristics are greatly affected.
Furthermore, in the related technology, in order to reduce the coupling capacitance, the drive wirings are arranged so as to be symmetrical to the two detection wirings. However, in this case, the lead-out of the wiring is limited, and the size of the mounting surface including the wiring is increased, and there is a problem in that the freedom of design of the angular velocity detection element, the signal processing element, and other elements, is reduced.
Moreover, in the related technology, since the lead-out of the wiring is limited and simultaneously the freedom of design of the elements is reduced, the angular velocity detection element is difficult to be flip-chip mounted on the substrate. That is, in order to flip-chip mount the angular velocity detection element on the substrate, the electrodes (wirings) must be disposed on the substrate side at high density in accordance with the electrodes on the element side and the wirings must be symmetrical in order to reduce the coupling capacitance. In contrast with this, in the related technology, since the lead-outs of the wirings are limited, high density wirings that are symmetrically arranged cannot be achieved. As a result, in the related technology, since an angular velocity detection element is mounted on the substrate using wire bonding, the common use in the mounting processing of components is impossible and the productivity is reduced, and crosstalk mixes through the coupling capacitance between the wires and there is a problem in that deviation of output at rest and offset temperature drift characteristics are deteriorated.